Chronic thromboembolic pulmonary hypertension (CTEPH) is associated with significant morbidity and risk for early death if left untreated. Treatment is by pulmonary thromboendarterectomy (PTE) for appropriate candidates. Almost nothing is known, however, about the variables associated with early mortality or long-term survival after PTE within a multivariate framework. We propose to develop and internally validate two prognostic indices, one for 30-day mortality and another for long-term survival after PTE, based on multivariate analyses using information that is readily available during the pre-, intra-, and post-operative 3eriods. It is hypothesized that the integrative measures of pre-operative pulmonary vascular resistance and post-operative total pulmonary resistance will be the most powerful predictors of outcome in the two prognostic indices, respectively. Statistical methods include univariate and multivariate regression techniques, including assessment of covariate time-dependence, and survival analysis. The resulting prognostic indices can potentially be used for pre- and post-PTE risk stratification. This research will be incorporated with formal training in epidemiology and biostatistics as part of a M.P.H. program.